ASSESSMENT OF THE POTENTIAL HEAT STORED IN THE DEEP AQUIFERS OF THE WILLISTON BASIN FOR GEOTHERMAL ENERGY PRODUCTION

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Abstract

As the world shifts from fossil based energy generation towards
renewable energy, it is important to consider the role geothermal energy can play in Saskatchewan. The deep reservoirs of the
Williston Basin possess some geothermal qualities that can be harnessed for direct purpose (heating and cooling of buildings) and for electrical power generation. Previous studies have looked at this potential at a large scale, however, this research focused on the moderate temperature geothermal resources (80-150oC) within two deep reservoirs, one formed by the Deadwood and Winnipeg formations of the upper Cambrian to Mid-Ordovician age and another
consisting of the Red River and its stratigraphic equivalent, the Yeoman Formation of the Upper
Ordovician age. This thesis uses the production and injection data acquired from the numerous hydrocarbon and waste disposal wells within Saskatchewan to quantify the probable heat and thermal power associated with hot waters historically produced at the basin scale. The research quantified electrical geothermal power within the reservoirs using three different techniques:
1) observed production rates; 2) maximum production rates (using well hydraulics); and 3) rock thermal volume.
For the first technique, the production or injection rate for each well within the reservoirs of Deadwood-Winnipeg and Red River-Yeoman was extracted from well production or injection
history data. A simple thermal equation was used to estimate the thermal power that could be
generated from each well. The results show that, on average, each well within the DeadwoodWinnipeg
reservoir and Red River-Yeoman reservoirs can generate thermal power valued at 0.4 MWt and 10 MWt respectively. The second technique used the well hydraulics, core analysis data and literature values to calculate the maximum possible values for production rates using the Cooper-Jacob empirical equation. The Gringarten and Sauty model was used in conjunction with these results to determine the required well spacing. The results show that the average well within
Deadwood-Winnipeg and Red River-Yeoman reservoirs can generate thermal power of about 101
and 105 MWt respectively. The final method estimated the geothermal power by calculating the volumetric heat capacity of the geothermal reservoir with respect to the area of the reservoir between the production and injection wells, thermal properties and the thickness of the reservoir. The results show that, on average, the entire reservoir based on the Gringarten and Sauty estimate for well spacing has the capability of generating geothermal power of about 170 MWt for sandstone (Deadwood-Winnipeg) and 286 MWt for the carbonate (Red River-Yeoman) reservoirs. This method overestimated the geothermal power that can be generated from the entire volume of the reservoir based on well spacing. However, when a recovery factor is added into the equation, it gives values that are reasonable and comparable to those estimated from theoretical
production.